The present invention relates to an abnormality determining apparatus of a fuel vapor processing system discharging a fuel vapor generated within a fuel tank to an engine intake passage.
As is well known, the fuel vapor processing system introduces a fuel vapor generated within a fuel tank into a canister through a vapor passage, temporarily reserves the fuel vapor by collecting by the canister, and discharges the collected fuel vapor appropriately to an intake passage of an internal combustion engine through a purge passage from the canister.
Further, as disclosed in Japanese Laid-Open Patent Publication No. 2004-301027, there has been well known an abnormality determining apparatus determining whether or not there is generated an abnormality (a leak abnormality) that a gas containing a fuel vapor leaks to the outside due to a perforation or the like in a fuel vapor path constituted by the vapor passage, the canister, the purge passage and the like.
The abnormality determining apparatus is provided with a pump connected to the fuel vapor path mentioned above. Further, at the time of executing the determination of the leak abnormality, an air is discharged to the outside from an inner side of the fuel vapor path in a closed state through an operation of the pump, and a pressure (an actually measured pressure) of the fuel vapor path is compared with a predetermined determination pressure. A pressure of the fuel vapor path at this time is lowered little by little to a predetermined pressure determined by a performance of the pump, a volumetric capacity of the fuel vapor path and the like so as to be stabilized unless the air makes an intrusion into the path from the outside.
On the basis of this point, in the abnormality determining apparatus, in the case that the actually measured pressure becomes equal to or less than the predetermined determination pressure, it is determined that the pressure of the fuel vapor path is sufficiently lowered, and the air does not make an intrusion into the fuel vapor path from the outside, or the air at such a degree that the abnormality determination is necessary does not make an intrusion, thereby determining that the leak abnormality is not generated. On the other hand, in the case that the actually measured pressure does not become equal to or less than the predetermined determination pressure, it is determined that the pressure of the fuel vapor path is not sufficiently lowered, and the air makes an intrusion into the fuel vapor path from the outside, thereby determining that the leak abnormality is generated.
In this case, the abnormality determining apparatus mentioned above is structured such that the air passing through the canister, in other words, the purified air that the fuel vapor is collected through the operation of the pump, is discharged to the outside from the fuel vapor path.
In this case, as the canister mentioned above, a canister is employed that has a structure in which the fuel is collected by adsorbing the fuel vapor (a vapor-phase fuel) while condensing to a liquid-phase fuel. Accordingly, at a time when the fuel is collected to the canister, the pressure within the canister and thus the pressure of the fuel vapor path are suddenly lowered in correspondence to the sudden reduction in the volume of the fuel due to condensation of the fuel.
Accordingly, in the abnormality determining apparatus mentioned above, if the determination of the leak abnormality is executed under a condition that a lot of fuel vapor exists within the fuel tank, the fuel vapor is introduced to the canister from the fuel tank through the operation of the pump, and the pressure of the fuel vapor path is suddenly lowered. Further, if a residual volume of the fuel vapor within the fuel tank becomes small thereafter, and the amount of the fuel vapor introduced into the canister becomes small to some extent, a pressure decrease amount caused by the condensation of the fuel becomes small, and a pressure decrease speed of the fuel vapor path becomes lower.
At this time, in the case that the leak abnormality does not exist in the fuel vapor path, the air within the fuel vapor path is discharged to the outside through the operation of the pump and the pressure of the fuel vapor path keeps lowering. Therefore, the pressure subsides to the predetermined pressure mentioned above.
In contrast, in the case that the leak abnormality exists in the fuel vapor path, the pressure of the fuel vapor path shifts to an ascent by a pressure increase amount caused by an intrusion of the air into the fuel vapor path. Accordingly, the change of the pressure thereafter subsides to a higher pressure than the predetermined pressure. As mentioned above, in the abnormality determining apparatus, in the case that the determination of the leak abnormality is executed under the condition that the pressure of the fuel vapor path is unlikely to be lowered due to the existence of the leak abnormality, the pressure of the fuel vapor path can become lower due to the condensation of the fuel within the canister only temporarily.
Further, if the temporary decrease of the pressure of the fuel vapor path is generated and the actually measured pressure becomes equal to or less than the predetermined determination pressure, it is erroneously determined that the leak abnormality is not generated in the fuel vapor path. As mentioned above, in the abnormality determining apparatus mentioned above, the temporary decrease of the pressure of the fuel vapor path mentioned above contributes to the reduction of a determination precision about the determination of the leak abnormality.